Justin Bieber, Selena Gomez "Happy and In Love" Over Dinner in NYC

Justin Bieber and Selena Gomez were most decidedly back on -- for one romantic dinner past midnight at NYC's Marble Lane, at least.

Strolling in around 1 a.m. Nov. 28, Bieber, 18, and Gomez, 20, took their own table and looked "happy and in love," one witness told Us Weekly of the pair, who have been off and on ever since their Oct. 31 split.

"Giggling, like nothing ever happened," the observer marveled, adding that the singers were "grabbing each other, joking." (Gomez began her evening in the Big Apple without her famous boyfriend, making an appearance at the Unicef Ball alongside Katy Perry and Uma Thurman.)

Another Marble Lane witness confirms their lovey-dovey meal a deux. "They were flirting and looked so happy together," the spy says. "When it came time to leave, Justin held her hand and looked very protective of her. It was sweet."

"I am all about genuine people, and I feel like she's just one of the most genuine people," Bieber told Oprah Winfrey in an interview taped before their romantic drama went down. "She just has a good heart. And I can talk to her about anything."